1. Field of the Invention
The present invention relates to a broadcasting receiver and a method of receiving a broadcasting wave, and more particularly, to a broadcasting receiver and a method of receiving a broadcasting wave, which controls an amplitude of a received signal.
2. Description of the Related Art
Broadcasting services using broadcast satellites and communication satellites are now provided, and in addition to these services, digitalized terrestrial broadcast is scheduled to start its service.
FIG. 8 is a view showing a receiving circuit in a conventional digital TV receiver. FIG. 9 is a view illustrating an electric wave distribution of analog waves (16 channels) and digital waves (8 channels, Channel Nos. 20 to 27) in Kanto area (a local area in Japan).
In FIG. 8, RF-AMP (radio-frequency signal amplifying circuit) 21 receives and amplifies a radio-frequency signal from an antenna, and outputs the amplified radio-frequency signal to MIXER (mixer circuit) 22. MIXER 22 mixes the radio-frequency signal received from RF-AMP 21 with a local oscillation signal supplied from a local oscillation circuit (not shown) to generate a low frequency signal. IF-BPF (low frequency band pass filter circuit) 23 receives and filters the low frequency to allow a signal falling within a predetermined frequency band to pass through. IF-AMP (low frequency signal amplifying circuit) 24 receives and amplifies the low frequency signal from IF-BPF 23. Gain of IF-AMP 24 is controlled by a feed back signal supplied from a demodulation circuit (not shown). RSSI•Filter (electric field intensity filter circuit) 25 generates a feed back signal corresponding to the low frequency signal received from MIXER 22 and supplies the feed back signal to RF-AMP 21 to control its gain.
In the receiving circuit shown in FIG. 8, since RF-AMP 21 receives analog waves in addition to plural digital waves, RF-AMP 21 is supplied with the feed back signal generated by RSSI•Filter 25 based on the electric field intensities of all the received waves. When some digital broadcasting channel is received at an area covered by a frequency band covering 8 channels of digital waves (channel 20 to channel 17) as shown in FIG. 9, an interference can be caused by adjacent channel waves, since the adjacent channel digital waves and/or analog waves are received in addition to the tuned in broadcasting channel wave. In other words, even though the user's tuned in channel wave is received, other adjacent channel waves are received to interfere with a receiving operation of the broadcasting wave in the broadcasting receiver.
To overcome the adjacent channel interference, there has been proposed a broadcasting receiver and a method of receiving a broadcasting wave in Japanese Laid-open Patent Application No. 2004-229170 (Patent Document #1). The broadcasting receiver is provided with a subsidiary tuner in addition to a main tuner to effectively attenuate a signal level of inter-modulation interference and to suppress drop in the received signal level of the tuned in broadcasting wave. While the main tuner receives the broadcasting wave and the wave is demodulated, the subsidiary tuner detects a state of the broadcasting wave, and controls the receiving operation of the main tuner based on the detection result. More specifically, the subsidiary tuner detects two inter-modulation interference broadcasting stations with respect to the tuned in broadcasting station, and when a difference between either of frequencies of the two inter-modulation interference broadcasting stations, which is closer to the frequency of the tuned in broadcasting station, and the frequency of the tuned in broadcasting station is not larger than a first previously set value, a tuning frequency control unit makes a tuning frequency of a tuning circuit more apart from the interference frequency. When such difference is larger than or equal to a second set value which is larger than the first set value, the tuning frequency control unit makes the tuning frequency of the tuning circuit closer to the interference frequency.
However, the broadcasting receiver provided with two tuners (main tuner and subsidiary tuner) as disclosed in the Patent Document #1, invites such disadvantages that manufacturing costs increase, power consumption raises, and the receiver is hard to make compact in size and light in weight. The digital terrestrial broadcasting will provide service for mobile communication terminals such as cellular phones, too. Therefore, the above disadvantages of the broadcasting receiver need to be solved. That is, the disadvantages that increase power consumption and make it hard to manufacture compact in size and light in weight are the problem to be solved first for enjoying services brought by the digital terrestrial broadcasting. It is not preferable to bring in the above disadvantages in order to solve frequency jamming problems.
The present invention has been made to solve these problems involved the conventional broadcasting receivers, and has an object to provide a broadcasting receiver which is made compact in size and light in weight, and further is capable of effectively reducing signal levels of the interference broadcasting stations and preventing drop in a signal level of a broadcasting wave to be intended to receive without increasing power consumption and manufacturing costs, and also to provide a method of receiving a broadcasting wave, used in such broadcasting receiver.